1. Technical Field
This present invention relates to a surface acoustic wave device and a manufacturing method thereof, and in particular, relates to a surface acoustic wave device and a manufacturing method thereof, including an auxiliary section for preventing contact between an IDT electrode and a cover substrate.
2. Related Art
Generally, such a surface acoustic wave device has been known, that a surface acoustic wave chip is composed of IDT electrodes, extraction electrodes, and anode junctions disposed in a manner to surround these IDT electrodes and extraction electrodes, in which the IDT electrodes, the extraction electrodes, and the anode junction are placed on a piezoelectric substrate. In such the surface acoustic wave device, furthermore, an insulating cover substrate is composed of a glass plate having an air gap and through holes formed therein, the external electrodes formed to the through holes and peripheries of the through holes, and printed electrodes formed beside the external electrode. Yet further, the extraction electrode of the surface acoustic wave chip is bonded to the external electrode of the cover substrate while the anode junction is bonded to the cover substrate to seal the IDT electrode.
Furthermore, such an surface acoustic wave device has also been proposed, as composed of a cover substrate not formed with the air gap and a surface acoustic wave chip un which a film thickness of an extraction electrode and an anode junction set to about 3 μm thicker than that of the aforementioned extraction electrode and anode junction. In such the surface acoustic wave device, the air gap is formed between the IDT electrode and the cover substrate by the extraction electrode and the anode junction.
JP-A-8-213874, see page 3 through page 5 and FIGS. 1, 3, and 8, is an example of related art
With the aforementioned structure such as described in the above example, in which the air gap is formed at the cover substrate, the air gap is formed at the cover substrate such that the IDT electrode and the cover substrate are not brought in contact with each other even where they become distorted by an externally applied force. With this structure, therefore, the whole cover substrate is necessary to be made thick to ensure strength thereof, which is unsuitable for the slimming down of surface acoustic wave devices.
Furthermore, with the structure in which the extraction electrode and the anode junction are made thick to ensure the air gap between the IDT electrode and the cover substrate, it is conceivable that the cover substrate and the IDT electrode are undesirably brought in contact with each other in the case of, e.g., occurrence of distortion in a center position of the cover substrate. Yet further, with this structure, a reflector or a reflecting barrier which are formed to a general surface acoustic wave chip, cannot be disposed since the extraction electrode is disposed at each end of the IDT electrode in a surface-wave direction, and thus it is estimated that the exact resonant frequency cannot be obtained.